# Promoter sum matrix
The Annotate regions task in Flow labels individual peaks as promoters for a particular gene if the peak falls 1000 bases upstream from a gene's transcription start site, or 1000 bases downstream from a gene's transcription start site by default. A promoter sum for a given gene is the number of cut sites per cell that fall within all the peaks labeled as promoters (-1000bp \~ 1000bp by default or user defined through Annotate regions) for that gene. Higher promoter sum values indicate higher chromatin accessibility in the promoter region \[1].
Flow task **Promoter sum matrix** summarizes each promoter sum and outputs a cell x gene matrix. In the matrix, only genes that have peaks within its promoter region have been included. In Flow **Promoter sum matrix** can be invoked in the Peak analysis section by clicking the Annotated regions data node (Figure 1).
Figure 1. Promoter sum matrixtask in Peak analysis section in Flow.
To run **Promoter sum matrix** in Flow,
* Click the **Annotated regions** data node
* Click the **Peak analysis** section in the toolbox
* Click **Promoter sum matrix**
Once the task has been finished, a new data node will be produced where the promoter sum value for each feature can be used to color UMAP/T-SNE and to determine cell type (Figure 2).
Figure 2.Output of Promoter sum matrixtask in Partek Flow.
## References
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